Stable- and some radioisotope-labeled compounds have been synthesized to support other laboratory projects. Structural analogues of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were prepared; oxygen-18-labelled-quinolinic acid prepared by exchange for use as an internal standard; synthetic routes for labelled tryptophan and its metabolites are under study.